Basic density of radiata pine in New Zealand: genetic and environmental factors
Wood basic density is among the selection criteria for many fast-grown tree species, including Pinus radiata D. Don in New Zealand. Basic density was assessed in 23,330 stem cores from 18 trials to study the heritability, the relevance of environmental effects and the magnitude of genotype-by-environment (GxE) interaction. Site differences in annual average temperature dominated variability in this dataset, with lower latitude and altitude (i.e. warmer) sites displaying higher average density. Between highest- and lowestdensity sites there was an 18% difference (302.7 vs. 358.4 kg m-3) for the linear mean for cores of rings 1–5 and a 39% difference (329.7 vs. 459.1 kg m-3) for the linear mean of rings 6–10. The estimated heritabilities fluctuated between 0.28 and 0.94 (mean, 0.6); however, basic density displayed little within-site variability (phenotypic coefficient of variation, <8%). Bivariate analyses were used to estimate between-site genetic correlations as an indication of GxE interaction. Only 57 out of the 153 pairs of trials contained enough information to estimate the between-site genetic correlations and, out of those, 15 estimates were not statistically significant. Moderate to high (0.46–0.96) significant genetic correlation estimates indicated that there was little interaction for basic density, suggesting no need to modify the breeding strategy to account for differential performance in this trait. Poor connectedness between trials could be depressing estimates of genetic correlations. This situation should be considered when designing genetic testing schemes, particularly when purposely inducing imbalance as in rolling front strategies.